1. Field of the Invention
The present invention relates generally to a system for detecting deterioration of the catalyst in a catalytic converter. More specifically, the invention relates to a deterioration detecting system suitable for detecting a deteriorating condition of a catalyst in a catalytic converter of an automotive internal combustion engine.
2. Description of the Background Art
In the recent days, requirements for anti-pollution performance are becoming much more strict than the past days. For answering such very strict requirements for anti-pollution performance in an exhaust system of an automotive internal combustion engine, various approaches have been taken. One of the important strategies in answering these anti-pollution requirements is the providing of a catalytic converter in an exhaust system of the engine for removing pollutants, such as CO, NOx and so forth. In order to achieve high level anti-pollution requirements, it is essential that the catalyst in the catalytic converter operates effectively, otherwise high level anti-pollution cannot be achieved.
Japanese Patent First (unexamined) Publication (Tokkai) Showa 56-88919 discloses a system for detecting an exhaust gas temperature to alarm of excessively high exhaust gas temperature. The disclosed system has an exhaust gas temperature sensor disposed within the catalytic converter for monitoring the exhaust gas temperature in the converter. The system detects excessively high temperature of the exhaust gas to activate an exhaust gas temperature warning indicator.
As will be appreciated, the Showa 56-88919 system simply detects excessive exhaust gas temperature to alarm of high exhaust gas temperature, since high exhaust gas temperature leads to damaging of the catalyst in the catalytic converter.
However, the shown system does not monitor the condition of the catalyst itself. In such a system, although extraordinary exhaust gas temperature can be detected, it is not possible to discriminate whether the abnormal temperature is caused by deterioration of the catalyst or cause by other reasons.
The applications has become aware that when the catalyst acts ineffectively due to deterioration, the exhaust temperature becomes lower. Therefore, it was found that by detecting extraordinarily low exhaust temperature, the deterioration condition of the catalyst can be detected so as to alarm of ineffectiveness of the catalyst.